Continuous Subcutaneous Insulin Infusion (CSII) is the basis for a state-of-the-art therapy of insulin-dependent diabetes mellitus. In this therapy, a diabetic patient carries a miniaturized infusion pump night and day and preferably concealed from view. The infusion pump administers insulin by a cannula, (the cannula oftentimes being made from medical-grade stainless steel or Teflon), into the subcutaneous tissue. The insulin pump administers insulin in a continuous or quasi-continuous way according to a patient-specific and time-of-day dependent basal profile in order to cover the patient's basal (i.e., meal-independent) insulin need. In addition, the pump is adapted to administer comparatively large insulin boli on demand which are required for covering the intake of food, namely carbohydrates, and to correct for undesirably high blood glucose values. Infusion devices which are adapted for the CSII therapy of diabetes mellitus are disclosed.
A general concern associated with the diabetes therapy based on insulin administration is the danger of hypoglycemia. While the number of potential reasons for this phenomenon is high, it is usually associated with a mismatch between blood glucose level and blood insulin level, with the blood insulin level being too high. The effect of hypoglycemic conditions may vary from a lack of concentration to severe perceptual disturbances, to coma and finally to death. Under normal circumstances, the immediate intake of fast-acting carbohydrates is a sufficient measure. However, in some cases, a diabetic may fall into a hypoglycemic coma very fast without having a chance to act properly.
In a situation of hypoglycemic coma, it is highly desirable to provide an alarm signal in order to get emergency support as fast as possible. It is further desirable to stop drug administration almost immediately in order to not worsen the situation. Therefore, state-of-the-art insulin pumps may comprise a ‘dead man’s control, which automatically triggers the generation of an audible alarm signal and stops insulin administration if no user interaction with the pump has occurred for a given alarming time in which a user interaction, such as a bolus administration, can be assumed to occur. In order to avoid false alarms, the alarming time may, for example, be as along as 12 hours. This is, however, often found to be inappropriate in different ways. On the one hand, the alarming time may be too short. When sleeping longer than normal (e.g., during the weekend), even a rather long alarming time may be too short and cause false alarms. Such false alarms are generally inconvenient and are even found to be dangerous if insulin administration is stopped due to a false alarm. On the other hand, the alarming time may be too long. If the situation of a hypoglycemic coma occurs shortly after a user interaction, alarming and potentially stopping the insulin administration are triggered only with a delay of many hours.